The invention relates to a line system and to a process and/or an apparatus for producing such a system, which in particular has a capillary tube as the fluid-carrying line section and components or assemblies connected thereto, the connection generally being a hermetically tight connection point, which does not interrupt the line system in its vicinity.
Such systems can be used as hydraulic control members in manually adjustable regulating means for electrical or other thermal equipment, such as electric hotplates, baking oven heating systems, continuous heaters, etc. The expansion liquid enclosed in pressure-tight manner with respect to the outside fills the interconnected areas in a complete, gas-free manner. An area on one end of the capillary tube is widened compared with the internal cross-section of the latter and can be formed by a separate, tubular jacket of a temperature sensor, whereas a corresponding, but appropriately smaller volume area at the other end of the capillary tube is formed by a casing, which as a function of volume changes with respect to said area has a movable actuator for at least one contact, a mechanical control member or the like. Fluid expansions in the temperature sensor lead to fluid displacements from the temperature sensor via the capillary tube into the casing area, and conversely, fluid compressions in the temperature sensor via the capillary tube lead to the reduction of the fluid volume in the casing space. The capillary tube can have a length of at least a half a meter or more than two meters and can be connected by means of a branch to a further capillary tube section. As a result of its flexibility, resilient characteristics, metallic characteristics, small external diameter of roughly one or a few millimeters and its smooth surface nature, the capillary tube is very difficult to handle in the manufacture of the system and during its installation.
In addition, the production of joints and their permanent sealing can be problematic. If the joints are soldered in the vicinity of an outer face of a connecting piece receiving the capillary tube, then most of the adhering solder is freely accessible to the atmosphere, so that there is a risk of rapid damage by corrosion to the soldered joint, particularly at elevated operating temperatures. The material differences between the soldering material and the parts to be soldered contribute to this. It is also very difficult to check a soldered joint with respect to its quality or seal, strength, freedom from gaps and cracks, etc. Some parts, e.g. a tubular temperature sensor, could be shaped in one piece from the capillary tube, but then the manufacture of differently constructed combinations of capillary tubes and sensors is made more difficult because one component cannot be connected in random manner to different other components.
For the mass production of such hydraulic systems, it is particularly appropriate to solder the joined components continuously when passing through a soldering furnace or by high frequency heating, but all components to be previously interconnected in accordance with the assembly sequence must be completely exposed to a relatively high heating, which is not favorable for protective hoses, springs, etc., because their material characteristics will change under the action of heat. It has also been found that soldering leads to an embrittlement of the capillary tube material at the joints. Other joining methods, such as plasma or laser welding, bring out scarcely any changes if the joints in the vicinity of said outer end are located at the intake of the capillary tube in a hole, in whose vicinity the capillary tube is normally exposed to maximum bending or alternating loads. An anti-kink device, such as a sleeve, shoved over the joint following the manufacture of the fused joint scarcely obviates this problem, because it can only act against significant bending deflections and only at a distance from the most critical areas of the joint.
If the capillary tube is directly connected to the actuator, then as a result of operation, it performs countless micromovements with the travel of the actuator, which can lead to a fatigue failure of the capillary tube, particularly if it is embrittled in this area by the manufacture of the joint. This can be admittedly counteracted by a curved capillary tube section connected to said joints, but said curved section increases the depth of the associated switching appliance. In addition, the curvature of the capillary tube can only start following the soldering material which, as a result of the adhesion action during the molten state, creeps by e.g. 1 to 2 mm from said outer face and along the outer capillary tube circumference and after cooling forms a corresponding stiffening sleeve intimately connected to the capillary tube. Such soldering processes are also problematic from the ecological and industrial medical standpoints, because high energy expenditure is required and health damage can only be prevented by expensive ventilation of the working areas and rooms.